It is well-known that biological tissue can be ablated by applying laser energy without substantial thermal damage of the target areas. This quasi non-thermal process is used for example in medicine for the treatment of cartilage, dental hard tissue, skin areas and also during eye surgery for sculpting the cornea (Photorefractive keratectomy, PRK). Such procedures and the associated device have been published for example in patents DE 197 27 573 C1 and EP 0 412 789 B1. A further procedure, in which the cornea is altered by lasers, is in-situ laser keratomileusis (LASIK). In contrast with PRK, a cut is first made into the cornea and a so-called “flap” is produced, which is folded away during the laser procedure in the work area. After concluding the ablation, which takes place thereby within the cornea, the flap is again folded back.
It is unfavorable that the residual products from the tissue ablation affect the air quality in direct proximity of the treatment place in the form of smoke or tissue particles, which leads to an unpleasant odor for the patient and the treating personnel, and on the other hand that the laser radiation is partially weakened. The latter has a particular relevance in the photorefractive keratectomy, with which the cornea surface is formed by a precise material removal which depends on an unhindered, application of the laser beam, and the fact that the radiation energy is accurately applied with a continuous intensity into the cornea, so that the ablation result can be obtained in the desired quality. The intensity is influenced (reduced) the laser beam produced smoke, vapors and tissue particles, which can lead to irregular and thus unwanted changes in the ablations. In LASIK there also exists the additionally danger that tissue particles may settle on the flap, leading to contamination and degradation of the optical quality.
U.S. Pat. specification No. 5,344,418 describes an implementation in which an applicator is placed close to the outlet of the laser beam with flow channels for gases and/or air, from which during the treatment a gas and/or an air flow may be directed towards the treated tissue, which has as intended consequence that the undesired ablation residual products are blown away from the treatment area.
Hereby the problem of air pollution and unpleasant odor for the patient and operating surgeon is yet not solved.
Also, the technical solution stated in U.S. Pat. specification No. 5,181,916 is not able to eliminate the mentioned disadvantages. Here no gas flow is directed toward the treated area by which the impurities are blown away. Instead the residual gases developing at the treatment place are drawn off with the help of a gas flow. An opening for this purpose is concentrically arranged around the aperture through which the laser beam is directed. This solution has the disadvantage that the visible treated area is only reduced during the treatment since it is partially covered by the opening.
On the applicant's patent DE 100 20 522 A1, the residual products are sucked from the ablation over a channel arranged over the ablation area, and at the same time a withdrawal duct is concentrically arranged around a flushing gas feeding line. This device also covers the treatment area in this case.
This disadvantage also exists in patent DE 101 29 650 A1, in which a circular flow channel is radially and symmetrically arranged around the ablation area, and the gas flow is directed by the discharge openings arranged on the ablation area. Thus the currents meet one another and interact in such a manner that a direction reversal and thus a radially arranged outward current are produced, which carry the ablation products and the developing smoke with them. The problem of the unpleasant odor for the patient and the operating surgeon is not solved in this case.